Method and apparatus to permit the boot of a shared memory buffer

Abstract

A method and system for allowing an arbitrary operating boot in a shared memory buffer architecture system. A chipset including a memory controller, a bridge, and an arbitration unit is used to control access to a shared physical memory. The physical memory is divided between the system memory and dedicated memory to be used by one or more devices. A portion of the physical memory is allocated as a dedicated memory for some system device. The remainder of the memory may be allocated as system memory. The allocation is performed by a system BIOS either at initial start up or through system BIOS calls made during initialization of the device to use the dedicated memory. Programmable bits in the chipset are programmed to prevent the memory controller from claiming dedicated memory accesses during the boot of an operating system. Since the operating system's attempts to write to the dedicated memory are not claimed by the memory controller during memory sizing, they are forwarded to an I/O bus. No 1/0 device claims these addresses, so a memory sizing read back is unanswered, and the operating system is caused to believe the top of memory has been reached below the dedicated memory. If the O/S does not do memory sizing, the system BIOS provides the O/S with the size of system memory available. Thus, in either case, the dedicated memory allocation is transparent to the O/S, and an arbitrary O/S may be employed with the system.